This application relates to fall arrest units, and, in particular to a fall arrest unit comprised of easily assemblable components.
Retractable fall arrests or lifelines have been used for many years and range in size from small (6 ft) units to large (175 ft) units. The purpose of a retractable lifeline or fall arrest unit is to allow workers, who must work on the leading edge of elevated surfaces (or other areas were falls are of concern) to have a means to attach to an overhead anchorage that will arrest their motion in case of an accidental fall. These retractables are usually equipped with a 3/16″ wire rope cable or a 1″ webbing lanyard of at least 4700 lb of anchorage strength. The retractables are equipped with shock absorbers that will limit the forces of a falling worker to 900 lb or less during a fall arrest. These shock absorbers may comprise an internal mechanical clutch type or an external rip-stop type made of webbing. The internal clutch mechanisms usually comprise a stack of friction disks which are held under a known compressive force by preloaded Bellville springs. The internal clutch mechanism normally is activated by a centrifugal pawl mechanism only after the falling worker achieves a certain velocity. The advantage of a mechanical clutch type shock absorber over a webbing rip-stop type shock absorber is that the former will activate much more quickly, which reduces input energy and creates a lower fall arrest force by limiting the worker fall height.
One of the difficulties of using mechanical retractable shock absorbing lifelines is that they must be periodically inspected for damage and be retested to confirm that they are operating correctly. This is usually done yearly and requires each fall arrest unit to be returned to the manufacturer for this recertification service. The reason these units must be returned to the manufacturer is because they are mechanically difficult to service due to the precision setting required on the clutch assembly and the difficulty of unloading and removing the power retraction springs, which may be over 100 ft. long. This is both costly and time consuming, requiring the customer to purchase extra units that can be rotated out of service for recertification on a regular schedule.
These problems are greatly compounded when retractable units are used in off-shore work sites where the retractables will be exposed to a salt (and thus, corrosive) atmosphere. In such conditions, the retractable must be serviced and recertified after approximately four months. Further, when a retractable is being serviced, it is out of commission for about two months.